#include <stdio.h>
#include <math.h>

double out(float x1, float y1, float x2, float y2) {
    double length = 0;
    length = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    return length;
}

int main() {
    int n, k, i;                     //�������
    scanf("%d", &n);
    double outcome = 0;
    double a[10][2];                //a []k []i
    for (i = 0; i < n; i++) {
        for (k = 0; k < 2; k++) {
            scanf("%lf", &a[i][k]); //��������a[][]
        }
    }
    if (n != 2) {
        for (i = 0; i < n - 1; i++) {
            outcome = outcome + out(a[i][0], a[i][1], a[i + 1][0], a[i + 1][1]);
        }
    }
    outcome = outcome + out(a[0][0], a[0][1], a[n - 1][0], a[n - 1][1]);
    printf("%.2lf", outcome);
    return 0;
}
